The present invention relates to a vacuum arc electron source comprising a plasma source having an anode and a cathode facing each other such that they produce a plasma after an appropriate voltage difference has been applied between the anode and the cathode, an electron extractor device and a material-retaining device arranged between the extractor device and the plasma source.
Such an electron source is disclosed in the article "Grid-controlled plasma cathodes", by S. HUMPHRIES et al., in the "Journal of Applied Physics", vol. no. 3 (February 1985), pages 700-713.
According to this article, the material-retaining device is constituted by an ion control grid (ICG) provided in the plasma and being at the same electric potential as the plasma source, and the extractor device comprising an extraction cathode K constituted by a grid which is biased positive with respect to the plasma source as well as an electron collecting anode A. The ion control grid ICG has for its function to separate the ions of the electrons in the grid ICG--cathode K space, the electrons being extracted or not extracted as a function of the space charge in the extraction gap between the cathode K and the anode A.
Such a structure requires a pulsed operation of the plasma source and a more specific operating condition is, that the pulse length of the plasma must not be too great relative to the pulse length required by the electrons to avoid electric loading of the grid and electric breakdown.